A. Field of the Invention
The field of the invention is in the field of low-cost knockdown shelf systems wherein individual shelves are in the form of trays made of a low-cost material having relatively high strength such as fiberboard or paperboard and wherein the vertical spacing between the shelves or trays is provided by tubular posts at the four corners of the rectangular shelves or trays.
B. Description of the Prior Art
Senge, U.S. Pat. No. 925,538, granted Jan. 24, 1923, discloses the basic construction of three wooden or metal desk trays separated by posts which are accommodated in sockets at the outside of the trays near the four corners. The posts may be rods or tubes.
An improvement of this desk tray assembly which is found in most United States government offices uses metal die cast tubes to separate the metal trays and a flange is provided on the outside of the tubes to assure alignment of the trays. In short, the flanges serve to assure the vertical distance between the trays is the same at all four corners and that each of the trays is level and parallel to the base tray.
My prior U.S. Pat. No. 4,428,487, to Hepp, shows a sectional display in which angular corner posts engage grooved portions on the underside of plastic trays. In order to achieve alignment at the four corners in a vertical assembly of three to five shelves of the rack, a plurality of rib portions are provided to assure engagement and locking of the corners. The construction is very sturdy but does not meet the need of a low-cost rack which is used mainly for storing rather than for display but which still is capable of supporting heavy loads and does not require the use of relatively expensive molded plastic, wood, or metal for the construction of the trays or shelves.
An all plastic knockdown shelf assembly is on the market commercially which consists essentially of molded plastic trays having corner apertures, and tubular plastic posts fitting in these apertures resting on flanges which provide the desired vertical spacing of the rack used in display.
Paper trays are known for use in shelf storage and handling systems, for example, a paperboard tray constructed of a single blank used in handling and sorting mail, is shown in Pfaffendorf, et al, U.S. Pat. No. 3,784,083. However, such paperboard trays have not been heretofore used in an assembly in the type in my prior U.S. Pat. No. 4,428,487.
Constructions using sockets and tubes comparable to the commercially available desk trays have also been used for example in the U.S. Pat. No. 3,480,154, to Telfer, and the U.S. Pat. No. 3,053,397, to Bliss. Telfer supports only one side of the trays and uses half tubes. Bliss stacks his trays for relatively heavy loads such as vegetables.
Abatiell, Jr., U.S. Pat. No. 3,426,913 in FIGS. 3 and 5 shows a combination all divider shelf assembly having double sockets but these structures require locking devices to make them stable.
Butsch, U.S. Pat. No. 2,591,049 discloses a sectional rack for storing heavy stock which use I beams to support the load. However there is no concept of cross-bracing the beams.
Warren, U.S. Pat. No. 1,572,342 shows a special rack for spools of friction tape material used for brake linings in which a series of parallel X members pivot about a common vertical rod and the spools are placed in the spaces between the X members.
Nawman, et al, U.S. Pat. No. 3,172,542 shows a tray having a paper bottom which is reinforced by a cross brace.
Wentzel, U.S. Pat. No. 3,490,702, describes a disposable paper tray in which the bottom panel is made of paperboard and is reinforced by cross braces.